Incorporation of [3H]thymidine into DNA and of [35S]sulfate into sulfatides of oligodendroglial cells during development: Effect of malnutrition

Incorporation of [³H]thymidine into DNA and of [³⁵S]sulfate into sulfatides of oligodendroglial cells isolated from brain slices incubated with the radioactive precursor was studied in normal and malnourished rats at different ages. The pattern and the values of incorporation of [³H]thymidine into DNA were similar in both groups of animals. The maximum value of incorporation was observed at 7 days of age decreasing rapidly thereafter and leveling off between 18–21 days. In both groups of animals labeling of sulfatides attained a maximum at 18 days of age, showing similar values of incorporation up to that age. However, at 21 days of age; the values corresponding to malnourished rats were found to be 40% lower in comparison to controls. The results suggest that (a) proliferation of oligodendroglial cells stops at similar ages in normal and malnourished rats, (b) expression of sulfatide synthesis by oligodendroglial cells is similar in both groups of animals up to 18 days, and (c) the starved rats seem to be unable to maintain normal synthesis of these galactolipids throughout the entire period of active myelinogenesis.     

Neonatal malnutrition in the rat affects the delivery of sulfatides from microsomes and their entry into myelin

Brain slices from 18 day old normal and malnourished rats were incubated in the presence of [³⁵S]sulfate to explore its incorporation into sulfatides of a total brain homogenate and the appearance of labeled sulfatides in different subcellular fractions. While the incorporation of label into sulfatides of the total homogenate was similar in both groups of animals, in subcellular fractions separated on a linear sucrose density gradient, labeling of sulfatides in malnourished animals was relatively higher in the region corresponding to the microsomal fraction. Time course incorporation and pulse-chase experiments were carried out to explore the kinetics of labeling of microsomal and myelin sulfatides. In pulse-chase experiments, normal controls showed a decrease in the specific radioactivity of sulfatides in the microsomal fraction after the chase, which was not observed in malnourished animals, while the appearance of labeled sulfatides in the myelin fraction of the latter group of animals was found to be lower than in normals. These results suggest that in neonatal malnutrition there is a defect in the transport of de novo synthesized sulfatides towards myelin or/and a problem in the assembly of these lipids into the myelin membrane.     

Variants within the yeast Ty sequence family encode a class of structurally conserved proteins.

The Ty transposable elements of Saccharomyces cerevisiae form a heterogeneous family within which two broad structural classes (I and II) exist. The two classes differ by two large substitutions and many restriction sites. We show that, like class I elements a class II element, Tyl-17, also appears to contain at least two major protein coding regions, designated TYA and TYB, and the organisational relationship of these regions has been conserved. The TYA genes of both classes encode proteins, designated p1 proteins, with an approximate molecular weight of 50 Kd and, despite considerable variation between the TYA regions at the DNA level, the structures of these proteins are remarkably similar. These observations strongly suggest that the p1 proteins of Ty elements are functionally significant and that they have been subject to selection.     

3H-uridine labelling patterns and chromosomal polymorphism inDrosophila subobscura: J and U chromosomes

The³H-uridine labelling patterns in J and U polytene chromosomes ofDrosophila subobscura were determined. The analysis was carried out in two developmental stages and in two strains proceeding from the same geographical origin whose genotypes were: J_st/J_st; U₁₊₂/U₁₊₂ and J₁/J₁; U₁₊₂₊₈/U₁₊₂₊₈ respectively. It was observed that the labelling pattern coincided very approximately with the puffing pattern in the same stages and chromosomal arrangements. Comparison of the³H-Uridine incorporation patterns between chromosomal arrangements showed light quantitative differences. These results are discussed in relation to the inversion effect.     

The thermodynamics of complex formation of cyclic tetra-aza-tetracetic acids

Enthalpy changes for the complexation of alkaline-earth and transition metals with three cyclic tetra-aza-tetracetic acids (cDOTA, cTRITA and cTETA) were obtained by continuous titration calorimetry. From these values and free energy data, the entropy changes for the same reactions were derived. The results show that these complexes are stabilised by both favourable enthalpy and entropy changes, except those of Mg²⁺ and those of Sr²⁺ and Ba²⁺ with cTETA. Generally, the entropy changes for the reactions of the alkaline-earth metals are higher than for the reactions of the non cyclic polyaminocarboxylic acids, but for the reactions of the transition metals the entropy changes are comparable for the cyclic and non cyclic ligands. These results are discussed in terms of a model of ‘cage’ coordination of the metals.The enthalpy changes decrease with the increase in size of the tetra-aza ring (except in the case of Cu²⁺) but no specific cavity size effect is noticeable. Consideration of the temperature-dependent and temperature-independent contributions to ΔH supports the idea that the number of coordinated nitrogen atoms and carboxylate groups vary along the series.     

High density of transmembrane glycoproteins on the flagellar surface of boar sperm cells

Membrane halves of boar sperm flagella were produced by freeze-fracture and labeled in situ with concanavalin A and wheat germ agglutinin; the lectins were visualized with protein-gold complexes. Concanavalin A and wheat germ agglutinin binding sites partition with both protoplasmic and exoplasmic halves of the membrane. A high density of lectin marking was found on protoplasmic membrane halves; we conclude that the label corresponds to transmembrane glycoproteins that, on freeze-fracture, are dragged across the outer (exoplasmic) half of the phospholipid bilayer. Our demonstration of numerous transmembrane proteins in sperm flagella offers the structural setting for previous models on flagellar surface motility that postulate accessibility of motile membrane components to the submembranous cytoskeleton.     

Quantitative ultrastructural changes of the endodermal cells in the early chick embryo analysed by stereological methods

The ultrastructure of endoderm cells of the area pellucida has been analysed in the chick embryo by stereological methods. These cells show a specific subcellular evolution which can be correlated with several aspects of morphogenetic behaviour. The cell form coefficient (CFc) changes notably from stage 5 (0.683) to stage 8 (0.446) accompanying the transformation of this layer into a squamous epithelium. An increase of the nuclear surface density is observed and is discussed in relation to the control of nucleocytoplasmic interchange. The mitochondrial volume and surface densities remain constant (3.12% of cellular volume and 0.727 mitochondria/mu(3) respectively). The endodermal cells possess higher levels of vitelline reserves (lipid bodies, 6.97% and yolk droplets, 8.90%) than other cellular types of the chick embryo. This fact is discussed with respect to the role of the endoderm in the phagocytosis of yolk. The RER length density shows an increase that could be related to some specific changes of the extracellular matrix during this period, but this fact remains to be demonstrated in relation to changes of Golgi membranes.     

Ovarian response to active immunization against luteinizing hormone in the cow

Two experiments were conducted to determine whether active immunization against luteinizing hormone (LH) could lead to ovarian cyst development in the cow. In Experiment 1, cyclic beef heifers were randomly assigned to receive bovine LH (bLH) conjugated with ovalbumin (LH-immunized; n=4) or ovalbumin alone (control; n=5). Blood samples were collected at monthly intervals from the LH-immunized heifers to determine antibody titers. Heifers were observed for estrous behavior twice daily. All heifers were slaughtered 4 mo after initial immunization and ovaries examined for follicular status. In Experiment 2, mature dairy cows were immunized with bLH (LH-immunized; n=4) or ovalbumin alone (control; n=3). Weekly blood samples were collected from all cows for 26 wk and ovaries were rectally palpated. Sera from all of the LH-immunized heifers and cows had antibodies to LH. All of the LH-immunized animals stopped cycling 1 mo after immunization. In spite of the fact that serum follicle stimulating hormone levels were unaffected, ovarian cysts could not be found in either the LH-immunized heifers or cows.